High-frequency sound signaling



- p 1929- 1. B. CRANDALL ET AL. 1,708,938

HIGH FREQUENCY SOUND SIGNALING Filed Nov. 25. 1919 q I? Q 6 M15 p I aMei/40H 5 557293 fiztenterl Apr. 16, 1929.

UNITED rArs IRVING B. GRANDALL, .OF EAST ORANGE,

NEW JERSEY, AND MARION s. ESTES, or

NEW YORK,- N. Y., ASSIGNORS 'L O WESTERN ELECTRIC COMPANY, INCORPORATED,OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

HIGH-FREQUENCY SOUND SIGNALING.

Application flied-November 25, 1919. Serial No. 340,471.

This invention relates to high frequency sound signaling and moreparticularly to devices used in submarine signaling for receiving highfrequency sound and pro '5 ducing indications therefrom. .7

An object of the invention is to provide selective means for receivinghigh frequency sound-energy.

. Another object of the invention is to provide a microphone receiverfor receiving and responding to sounds of ultra-audible frequency.

I An additional object of the invention is to provide a microphonemechanically tuned 16- to sound energy. 0 a given high frequency. Afurther object 'of the invention is to provide a microphone capable ofresponding to high frequency sound waves in water.

A still further object of the invention is to provide a receiving systemfor high frequency submarine sound transmission.

According to this invention a solid back microphone is constructed with.a carbon movable front electrode which may be spherical. The movableelectrode is rigidly fixed to a thick metal diaphragm of such dimensionsas to have a natural period corresponding to that of the high. frequencysound waves to be received. a The tuned 3o microphone so designed actsto produce high frequency variations in an electric current passingtherethrough and these high frequency electric current variations "aredetected in well known manner.

Referring to the drawing, Fig. 1 illustrates diagrammatically a highfrequency submarine sound-receiving arrangement; Fig. 2 illustrates insection a tuned microphone receiver; Fig. 3 a section of a microphone;and Figs. 4; and 5 illustrate modified forms of the tuned diaphragmemployed in the construction of Fig. 2. p

In the receivin system of Fig. 1 a high frequency microp one receiver 1is s own in circuit with a source 2 of unidirectional current and theprimary winding of a transformer 3, the secondary winding of which is inthe input circuit of a detector 4 .of

high frequenc electrical currents. detector is pre erably of thethermionic discharge type. Associated with the input cir- This cuit ofthe-detector by means of a transformer 5 is a local source 6 of highfrequency electric currents which may be of the same frequency as thatof the sound waves to be received, as in the case of telephony; or maybe of a different frequency as in telegraphic or teledynamic controltransmission. 4 is connected in well-known manner to an amplifier 7 bywhich low frequency currents resulting from the detecting action areamplifiednnd supplied to a receiver 8 connected thereto.

In operation, the high frequency sound waves in water or other medium inwhich source 6. If heterodyne operation is to be employed the frequencyof source'6 will be made'difl'erent from that of the incoming sounds.For telephony, as explained in United States Patent No. 1,330,471,patented- February 10, 1920 to B. W. Kendall for high frequencysignaling, the current produced by the local generator will preferablybe of the same frequency as the incoming sound waves. The detector 4acts to combine the two electrical waves to produce in the outputcircuit a low frequency current component corresponding, in the case ofheterodyne operation, to the beat difference note of the twoelectromotive forces supplied, and in the case where the local source 6produces currents of the incoming wave frequency, telephonic or otherlowfre- The output circuit of detector be any signal receiving orindicating device or in the case of teledynamlc control transmission, aselecting or controlling element.

As shown-in Fig. illustrating the tuned microphoneu'eceiver, amicrophone casing 9 of conducting materiahhas secured there in by meansof insulating material 10-, such as wax or rubber, a stem portion of asolid ba K member .11 of a ll1lCI'Opl10IlG..

The front electrode or button 12 of the n1icro,-

' phone is attached by means of a-screw 18 to tuned diaphragm 14 whichis preferably of disc shape and is clamped against an annular seat bymeans of-clamping ring 16 and bolts 17, attaching said ring to the seatportion of the casing. Conducting ,leads 18 are introduced into thecasing 9 through an insulating sleeve 19. passing axially through athreaded bushing 20 of insulatingmaterial fitted in a' threaded recessin the casing. One of the leads is'el'ectrically connected to the casingand. the other to the stem of the back member of the microphone, so thatcur I compact shape insuring rigidity and fits into a central openingofwasher 23, to which it is attached by glue or other adhesive material25. Cup 21 is fitted interiorly with a cylindrical insulating member 26and inside of this vcup and-adjacent its back wall a thin carbon disc 27and a metallic disc 28 globular or of the'ordinary form are placedwithin the cup 21 and are retained by washer 23. The front electrode 12bears against the granules and because of its shape produces largevariations in pressure for slight displacements of the diaphragm.

- The diaphragm 14L maybe a plane disc, as shown in Fig.2, or may berecessed, as

indicated in Figs. 4 and-5. For high frequency operation the microphonereceiver may be made selective of a particular frequency by so designingthe diaphragm that it is mechanically tuned to the desired fre quency.In accordance with the well known laws of tuning 'of clamped plates thefrequency of the diaphragm may be made high by increasing its stiffnessand decreasing its mass. Consequently, material of low atomic mass suchas aluminum, may be used, and

.the diaphragm may be made relatively thick in' proportion to itsdiameter.

any

In the modifications of Figs. 4 and 5 the ,diaphragmis .shown centrallyrecessed so that the thickness at the. center is considertothe tuneddiaphragm and is made rigid and compact so that the electrode will beforced to partake of the high frequency movement of the diaphragm, andthe variations in the microphonic current will correspond in frequencyand in amplitude to the sound wave energy received.

In practice, operating at .a frequency of 80,000 cycles per second, thediaphragm has. been made ;of aluminum, the clamping ring having aninternal diameter of an inch. With the form 'of diaphragm shown in Fig.4, the minimum thickness of the diaphragm was made one-eighth of an.inch, and the' thickness at the periphery one-quarter of an inch. Thefront. electrode was a spherical carbon diameter.

' It is to be understood that the specific circuit and structuraldetails, as well asthe f The front electrode 12 is rigidly attached Iball; five-sixteenths v of an inch in I dimensions .recitedherein, aregiven merel 1 byway of example of aconstruction whic has been foundsatisfactory in practice, and that the invention is not to be' limitedthereto, but only by the scope of the appended claims.

.VVhat is claimedisz 1.' An acoustical 'dia hragm comprising a disc thethickness ofgwh ch varies symmetrically with respect to itscenter, saiddisc being composed of material of such atomic mass relatively to itsdiameter and thickness that, .when clamped at its periphery, itsubstantially excluslvely vibrates ata single superaudible frequency.are placed. Carbon granules 24 of semi- 2. A tuned highfrequencyacoustical diaphragm comprising an'alummum disc substantiallythinner at its center than at any other point and which has a generallylenslike form.

3. A tuned high frequency acoustical dia phragmcomprising a disc, thethickness of 415 which decreases progressively from its peripherytowards its center.

4. An acoustical diaphragm comprising a disc whose thickness variessymmetrically with respect to its center and is minimum at the center,the atomic mass relatively to the rial, a substantially sphericalconducting button, a thin flexible retaining member attached to saidbutton and serving to close -said cup, means insulating said button fromsaid cup except through said granular material, a tuned diaphragm rigidlconnected to said button, and terminal e ements attached to said buttonand said cup whereby a circuit may be completed therebetween and throughsaid granular material.

7. A solid back microphone sound receiver comprising a casing, a cupcontaining granular material rigidly attached thereto, a conductingbutton having a substantially spherical surface in engagement with saidmateria1, means insulating said button from said cup except through saidgranular material, a tuned diaphragm rigidly connected to said button,and terminal elements attached to said button and said cup whereby acircuit may be completed therebetween through said granular material.

8. A solid back microphone sound receiver comprising a rigid casingmember having a front opening, a diaphragm closing said opening, amicrophone carried thereby and secured at the back-of. said casingmember,

and means whereb said diaphragm may ac tuate said microp one, saiddiaphragm being of such atomic mass and relative dimensionsto be tunedto a definite superaudible' frequency.

In witness whereof, we hereunto subscribe our names this 19th day ofNovember, -A. D.

4 IRVING ORANDALL.

MARION s. ESTES.

